1. Field of the Invention
The present invention relates to an expansion valve which is provided in a refrigerating system to sense the temperature of the refrigerant delivered from an evaporator to a compressor and automatically control the flow rate of the refrigerant entering the evaporator.
2. Description of the Related Art
An expansion valve of the type described above is generally provided with a low-pressure passage having one end thereof connected to the outlet of an evaporator and the other end thereof connected to the inlet of a compressor to pass low-temperature and low-pressure refrigerant and another passage having one end thereof connected to the outlet of a reservoir accommodating high-pressure liquid refrigerant and the other end thereof connected to the inlet of the evaporator to adiabatically expand high-temperature and high-pressure refrigerant. In addition, the expansion valve is provided with a temperature-sensing chamber which senses the temperature of the refrigerant in the low-pressure passage and changes in pressure in response to a change in the refrigerant temperature to control the degree of opening of a valve provided in the passage for adiabatic expansion by the operation of the temperature-sensing chamber, thereby controlling the flow rate of the refrigerant supplied to the evaporator.
The above-described conventional expansion valve suffers, however, from the following problems. Since the temperature-sensing chamber is provided on the outer surface of the expansion valve unit, the chamber is affected by the ambient temperature, so that the flow rate control of the refrigerant is not always accurately effected and the response of the flow rate control to a change in the temperature of the low-pressure refrigerant is inferior.
In many cases, the temperature-sensing chamber is arranged such that a gas which is the same as the refrigerant circulated through the passage for adiabatic expansion and the low-pressure passage is sealed in the temperature-sensing chamber so that the chamber changes in pressure in response to a change in the pressure of the gas. In this case, the operating characteristics (temperature-pressure characteristics) of the temperature-sensing chamber are uniformly determined by the inherent vapor pressure characteristics of the sealed gas. For this reason, there have heretofore been cases where it is impossible to set temperature-pressure characteristics in conformity to each particular refrigerating system and hence impossible to effect optimal flow rate control of the refrigerant.
Since in the prior art the temperature-sensing chamber and the valve mechanism are individually assembled to the expansion valve unit from both sides thereof, it is not easy to assemble, disassemble and adjust the expansion valve and it is difficult to carry out maintenance. Therefore, when a trouble occurs, in many cases the whole expansion valve unit must be changed for a new one, which is considerably uneconomical.